The present invention relates to a stent with different mesh patterns, wherein a mesh pattern at least one end of the stent is different from that of a middle portion thereof.
"Stent", which is defined here as a prosthetic member used for reinforcing the blood vessel, has been used in the interluminal vascular treatment in place of surgical exposing, incising, removing, replacing or bypassing a defected blood vessel required in the conventional vascular surgery.
The stent generally has a tubular shape and functions to support a part of a blood vessel or another anatomical lumen from the inside thereof, and is particularly suitable for supporting and holding a dissected arterial lining which may occlude a fluid passageway by collapse thereof.
According to the recent new clinical data, however, the followings have been found as problems upon using the stent.
Firstly, when a stent is placed in a stenosis, it extends over the full length of the stenosis. Namely, a stent is placed to bridge the whole lesion starting from a healthy tissue, lesion, and then to another healthy tissue. When a stent, normally made of metal, contacts the coronary wall, micro thromboses may occur at the contact areas with healthy tissues. As a result, when the stent is placed to open and hold the lesion, there are more chances of thromboses occurring at both ends of the stent corresponding to the healthy tissues. This is because all stents currently known have a uniform pattern throughout the entire length thereof, i.e. the strength and expandability are the same throughout the entire length of the stent, including the healthy tissues.
In view of the formation of micro thromboses, the stent with less metal contact is preferable. However, it is also necessary to have more metal coverage against prolapse, i.e. excessive tissue growth passing through the stent.
Secondly, in the balloon expandable type of the stent, the stent in a closed condition is mounted on the balloon section of the balloon catheter, and delivered to the lesion or stenosis by the balloon catheter. When the stent in the closed condition has the same diameter throughout the entire length thereof and delivered through a meandering artery in and around the calcified lesion, a front end of the stent might be caught at the calcified lesion if the diameter at the end is not small enough for passing through the calcified lesion or the narrow artery.
In this respect, if the diameter of the stent in the closed condition is small, it is possible to pass the narrow artery. However, when the stent is expanded to have a large diameter, the expanded stent can not sufficiently support. On the other hand, if the expanded stent is made to sufficiently support the artery, the stent must have a large number of supports, so that the stent can not be expanded to have a large diameter.
Therefore, there is no conventional stent expandable by a balloon catheter, which has a sufficient support structure; can expand to have a large diameter; and can pass the narrow artery.
Accordingly, one object of the invention is to provide a stent in which a middle portion thereof has enough or maximum strength to open and hold the stenosis or lesion.
Another object of the invention is to provide a stent as stated above, wherein end portions of the stent do not hurt healthy tissues of the artery.
A further object of the invention is to provide a stent as stated above, which can be easily delivered through the meandering and narrow artery without being caught at the calcified lesion or the narrow artery.
Further objects and advantages of the invention will be apparent from the following description of the invention.